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Abstract

We investigated the joint influences exerted by the nonuniform aerodynamic flow field surrounding the optical dome and the aerodynamic heating of the dome on imaging quality degradation of an airborne optical system. The Spalart–Allmaras model provided by FLUENT was used for flow computations. The fourth-order Runge–Kutta algorithm based ray tracing program was used to simulate optical transmission through the aerodynamic flow field and the dome. Four kinds of imaging quality evaluation parameters were presented: wave aberration of the exit pupil, point spread function, encircled energy, and modulation transfer function. The results show that the aero-optical disturbance of the aerodynamic flow field and the aerodynamic heating of the dome significantly affect the imaging quality of an airborne optical system.

References

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Table 3.

Refractive Index Variations of the Center on the Outside Surface of the Dome and the Center on the Inside Surface of the Dome at 15 sa

Point

Δno

Δne

Δn1

Δn2

Δn3

Δn4

Δn5

Δn6

1

1.80×10−3

2.02×10−3

5.46×10−6

6.87×10−6

7.65×10−6

−2.32×10−7

8.75×10−9

2.93×10−9

2

1.64×10−3

1.84×10−3

5.29×10−7

1.28×10−6

1.59×10−6

−1.25×10−7

6.52×10−9

2.19×10−9

a Point 1 denotes the center on the outside surface of the dome. Point 2 denotes the center on the inside surface of the dome. Δno and Δne are the refractive index variations caused by the thermo-optical effect. Δn1, Δn2, Δn3, Δn4, Δn5, and Δn6 are the refractive index variations caused by the elasto-optical effect.

Tables (3)

Table 1.

Boundary Conditions for Aerodynamic Computation

Altitude (km)

10

Mach number (Mach)

3

Inlet total pressure (Pa)

26,435.8

Inlet total temperature (K)

223.15

Angle of attack (°)

0

Table 2.

Main Physical Properties of the Sapphire Crystal Near 300 K

Physical Properties

Performance Parameters

Density (kg·m−3)

3980

Melting point (K)

2323

Expansion coefficient (10−6K−1)

5.3

Heat capacity (J·kg−1·K−1)

750

Young’s modulus (109Pa)

344

Thermal conductivity (W·m−1·K−1)

36

Poisson ratio

0.27

Mean strength (106Pa)

300

Table 3.

Refractive Index Variations of the Center on the Outside Surface of the Dome and the Center on the Inside Surface of the Dome at 15 sa

Point

Δno

Δne

Δn1

Δn2

Δn3

Δn4

Δn5

Δn6

1

1.80×10−3

2.02×10−3

5.46×10−6

6.87×10−6

7.65×10−6

−2.32×10−7

8.75×10−9

2.93×10−9

2

1.64×10−3

1.84×10−3

5.29×10−7

1.28×10−6

1.59×10−6

−1.25×10−7

6.52×10−9

2.19×10−9

a Point 1 denotes the center on the outside surface of the dome. Point 2 denotes the center on the inside surface of the dome. Δno and Δne are the refractive index variations caused by the thermo-optical effect. Δn1, Δn2, Δn3, Δn4, Δn5, and Δn6 are the refractive index variations caused by the elasto-optical effect.